1. Field of the Invention
The present invention generally relates to an actuator for use in a locking mechanism. More particularly, this invention relates to a shift lock actuator for a shift lever in a vehicle automatic transmission mechanism, and to a drive control circuit.
2. Description of the Related Art
Locking actuators used in vehicles have several applications such as in the automatic transmission mechanism or doors. A conventional actuator includes a motor, a feed screw which in capable of rotating in the forward and backward, a nut which cooperates with the feed screw, a lock bar which is shiftable between a locking position and an unlocking position, and a control circuit for controlling the rotation of the motor.
This actuator however, requires a stopper for holding the lock bar in the locking position or the unlocking position, and a limit switch, for detecting the lock bar position. This conventional design renders the construction of the actuator more complicated, and increases its size. Furthermore, when the lock bar abuts the stopper, a sound is produced, and the stop position of the lock bar varies as a result of the bouncing reaction of the lock bar.
It has been a design objective to cause the shift lock actuator in an automatic transmission mechanism, more difficult to unlock in an emergency situation. Such a design would involve a complex mechanical structure and control circuit.
Because of the need to control the rotation of the motor, the conventional actuator requires a complex control circuit, similar to the one disclosed in the Japanese Unexamined Patent Publication No. 2-38146. In this control circuit, an output circuit supplies current to the motor, and includes a bridge circuit having four transistors. This bridge circuit complicates the control circuit, and increases the size of the shift lock actuator.